The IRA attack took place in July that year when, a car bomb left on South Carriage Drive killed four soldiers and seven horses as they rode through Hyde Park in Central London to the changing of the guard.
Parker-Bowles was leading the Queen's Calvary that day and described the moment the explosion took place in Robert Hardman's new book, Queen of the World.
"One of the barriers opened and someone said, "They've blown up the Guard". So we ran down to where the smoke was rising.
"The first horse I saw was Sefton. He had a bloody great hole in him but he managed to pull through."
Following the tragedy, Parker-Bowles spoke to Her Majesty and described her words as "She said to me it was "The most ghastly day of my life"."